Cardiac function and myocardial strain analysis at 7T using B1 shimming in comparison to 3T magnetic resonance imaging.

Due to spatial heterogeneities of transmit B1 magnitude, cardiac MRI at 7 Tesla is still far from being clinically established. Different strategies were proposed to mitigate signal variations that may lead to a significant increase of the examination time. The aim of this study was to establish an efficient workflow for B1 shimming for cine imaging at 7T with a single B1 shim set and the investigation of the impact of field strength on volumetric and strain parameters Long- and short-axis images were acquired in ten volunteers at 3T and 7T. At 7T, B1 maps were acquired to calculate a single B1 phases him vector that was applied for the entire exam. Image quality reading was performed by two radiologists. Biventricular volumetric parameters were assessed by two readers. Biventricular function was further assessed for peak strain using feature tracking Image quality and contrast of long-axis images acquired at 7T was inferior compared to 3T, although all images were deemed to bediagnostically usable. In comparison to 3T, 7T slightly underestimated left ventricular volumes, with differences remaining under 10%of absolute values and thus of minimal clinical relevance. Strain parameters were not impacted by field strength A single B1 shim set provides excitation patterns without substantial signal dropouts in the heart. Moderate residual B1 variations and the reduced myocardium-blood contrast at 7T hindered neither quantification nor diagnostic quality. In conclusion, an efficient workflow could be realized at 7T for cardiac cine imaging for function and strain analysis.